[Alyex227]

Try adding critical damage [hitting while falling].

Plus

A zombie has 20 hearts IIRC, don't know how much the swords do at IV or V, but as long as IV is more than 10 hearts of damage and less than 20 hearts of damage, if V is higher than IV even by 1 heart but is lower than 20 then it all checks out.

example

IV - 14 Hearts
V - 19 Hearts

If you add a critical attack to it, V should insta kill a zombie while IV shouldn't or if it does, then that makes Smite V an even moreso worthless enchantment than it was initially.